1. Field of the Invention
This invention relates to a method and an apparatus for recording and reproducing a radiation image, and more particularly to a method and an apparatus for recording a radiation image on a stimulable phosphor and reproducing the recorded radiation image utilizing stimulability of the stimulable phosphor.
2. Description of the Prior Art
As is well known in the art, a photographic film using a silver halide has generally been employed to record a radiation image. Recently, from the viewpoint of problems such as shortage of silver resource, a method for recording a radiation image without using a silver salt has been desired.
As a method which can take the place of the above-mentioned photography, a method for recording and reproducing a radiation image is known, which comprises the steps of (i) causing a stimulable phosphor to absorb a radiation passing through an object, (ii) stimulating the phosphor by a certain kind of energy to release the energy of the radiation stored in the phosphor as fluorescent light, and (iii) detecting the fluorescent light. For example, British Pat. No. 1,462,769 and Japanese Patent Laid Open No. 29,889/1976 disclose a method included in the above-mentioned method, wherein a heat-stimulable phosphor, viz, a thermoluminescent phosphor, and thermal energy are employed as the stimulable phosphor and the stimulation energy, respectively. That is, in the method disclosed in the above publications, a radiation image storage panel comprising a support base and a thermoluminescent phosphor layer provided thereon is employed, and a radiation image is recorded and reproduced by causing the thermoluminescent phosphor layer of the panel to absorb a radiation passing through an object to store therein the energy of the radiation corresponding to the intensity of the radiation, releasing the radiation energy stored as a light signal by heating the thermoluminescent phosphor layer, and then detecting the light signal. However, the kind of the materials employed in the thermoluminescent phosphor layer and the support base of the panel is severely limited, because the panel is heated in order to convert the radiation image stored therein to a light signal, and hence, it is absolutely required for the panel to be heat resistant (resistance to deformation or deterioration by heat). Accordingly, in view of the above limitation, it is considered to be substantially difficult to practically use the method disclosed in the above publications.
U.S. Pat. No. 3,859,527 discloses another method included in the above-mentioned method and an apparatus therefor wherein a visible ray- or infrared ray-stimulable phosphor and visible rays or infrared rays are employed as the stimulable phosphor and the stimulation energy, respectively. The method disclosed in the above U.S. patent is considered to be more preferable than that disclosed in said British patent and said Japanese patent, because the panel employed in the method of the U.S. patent is not heated but exposed to visible rays or infrared rays in order to convert the radiation energy stored therein to a light signal, and accordingly, it is not required for the panel to be heat resistant. However, as a visible ray- or infrared ray-stimulable phosphor which can be employed in the method, only several phosphors such as a cerium and samarium activated strontium sulfide phosphor (SrS:Ce,Sm), a europium and samarium activated strontium sulfide phosphor (SrS:Eu,Sm), a europium and samarium activated lanthanum oxysulfide phosphor (La.sub.2 O.sub.2 S:Eu,Sm) and a manganese and halogen activated zinc cadmium sulfide phosphor [(Zn,Cd)S:Mn,X, wherein X is halogen] are known. Further, the sensitivity in the method in which these phosphors are employed is very low because the stimulability of these phosphors is very low. Accordingly, from the viewpoint of the practical use of the method, the improvement of the sensitivity thereof is desired.